1. Field of the Invention
The present invention relates to a data recording and reproduction device such as a magneto-optical disk device or magnetic disk device. It also relates to a magnetic head used as a constituent component of such a data recording and reproduction device.
The term xe2x80x9cmagnetic headxe2x80x9d as used in this specification refers to a data recording and reproduction head equipped with a coil for generating a magnetic field, and is a concept encompassing a xe2x80x9cmagneto-opticalxe2x80x9d head equipped with an optical lens.
2. Description of the Related Art
FIG. 14 illustrates an example of a magneto-optical head. This magneto-optical head comprises object lenses 91a and 91b and a magnetic field generating coil 92, all mounted on a lens holder 90. The object lenses 91a and 91b focus laser light traveling from a laser light source, thereby forming a beam spot on a magneto-optical disk D. The coil 92 is used to apply a magnetic field at the place where the beam spot is formed, and may be provided on the lens surface of the object lens 91b that is across from the magneto-optical disk D. This configuration allows the coil 92 to be moved closer to the magneto-optical disk D. Accordingly, compared to a conventional design in which an optical head equipped with an object lens is provided separately from a magnetic head comprising a coil, the coil uses less electric power, and a low inductance type can be used, which is advantageous in raising the data transfer rate using a magnetic field modulation system.
With a magneto-optical head structured as above, the lower the inductance of the coil 92 is, the more the drive frequency of the coil 92 can be raised, and the higher the transmission rate can be. To lower the inductance of the coil 92, the magnetic field generated by the coil 92 must be made to act efficiently at the prescribed place on the magneto-optical disk D. In view of this, it has been proposed in the prior art that a magnetic substance (soft magnetic substance) be provided in proximity with the coil 92, thereby concentrating the flux of the magnetic field generated by the coil 92 in the center of the coil 92.
However, the following problems have been encountered with the above prior art proposal.
Namely, when the coil 92 is driven with alternating current, an eddy current (induced current) flows in the magnetic substance so as to cancel out changes in the magnetic field generated by this coil 92. This eddy current causes the magnetic substance to generate heat. Heat is also generated as a result of the hysteresis loss of the magnetic substance. The amount of heat generated by the magnetic substance due to the above factors increases sharply as the drive frequency of the coil 92 rises, and this, coupled with the heat generated by the coil 92 itself, ends up raising the temperature of the coil 92. In addition to being a cause of disconnection of the coil 92, this temperature elevation of the coil 92 also drives up the electrical resistance of the coil 92, leading to a vicious cycle whereby the heat generation of the coil 92 is accelerated even further. Also, when the laser light focused by the object lenses 91a and 91b passes through the center of the coil 92, the above-mentioned temperature elevation of the coil 92 deteriorates the optical characteristics of the magneto-optical head. Thus, the problem of heat generation is encountered when an attempt is made to drive the coil 92 at a higher frequency, and there is room for improvement in this respect.
The present invention has been proposed in light of these circumstances, and it is an object of the present invention to provide a magnetic head with which temperature elevation of a magnetic field generating coil can be suppressed while the drive frequency of the coil is raised, thereby achieving a suitably high data transfer rate. Another object of the present invention is to provide a data recording and reproduction device equipped with this magnetic head.
The present invention employs the following technological means for achieving the above objects.
According to a first aspect of the present invention, there is provided a magnetic head including: a coil for applying a magnetic field to a recording medium; and a first electroconductive film superposed over the coil in an axial direction of the coil so as to be electrically insulated from the coil, the film being formed with a central hole. The first electroconductive film is composed of a non-magnetic substance. Also, the first electroconductive film is formed with a first slit extending from the hole to an outer peripheral edge of the first electroconductive film.
This constitution makes it possible for the above-mentioned electroconductive film to serve as a heat-radiating member that allows heat generated from the coil to escape. Because this film is electroconductive, less heat will be generated as a result of electrical resistance when induced current flows in this film. Also, because the electroconductive film is a non-magnetic substance, heat generation due to hysteresis loss can be suppressed. This makes it possible to minimize the temperature elevation of the coil.
Meanwhile, although the principle will be described in detail below, as a result of providing the above-mentioned first slit, when induced current flows in the electroconductive film, induced current that would act to strengthen the magnetic field generated by the coil can be made to flow to the inner peripheral edge of the first electroconductive film. Therefore, not only is the magnetic field generated by the coil kept from being weakened by the induced current flowing in the first electroconductive film, but the above-mentioned magnetic field can actually be strengthened by effective utilization of the induced current. As a result, a coil with a correspondingly lower inductance can be used. Consequently, with the present invention, the coil can be driven at a high frequency while the temperature elevation of the magnetic field generating coil is suppressed, which contributes to a higher transfer rate.
Preferably, the first electroconductive film may be provided with a second slit surrounding an inner peripheral edge of the first electroconductive film and with a continuity component that electrically connects part of the inner peripheral edge of the first electroconductive film to a region of the film that is outside of the second slit. The principle behind this constitution will also be described in detail below, but this constitution makes it possible to move the center of the electroconductive film farther away from the place where induced current flows and acts to weaken the magnetic field generated by the coil, thereby further strengthening the magnetic field.
Preferably, the magnetic head of the present invention may further include a dielectric film that covers the coil and includes a surface facing the recording medium. The dielectric film electrically insulates the coil from the first electroconductive film. This constitution affords more secure electrical insulation between the coil and the first electroconductive film. It also results in the coil being suitably protected.
Preferably, the first electroconductive film may have a higher thermal conductivity than the dielectric film. This constitution suitably imparts a heat radiation function to the first electroconductive film.
Preferably, the first electroconductive film may have an outer diameter which is greater than an outside diameter of the coil. This constitution enhances the heat radiation function of the first electroconductive film in proportion to the increase in its volume.
Preferably, the magnetic head of the present invention may further include an object lens for forming a beam spot on the recording medium by focusing a light beam traveling from a light source. After passing through the object lens, the light beam reaches the recording medium via a light transmitting component formed in the center of the coil and via the hole formed in the first electroconductive film. This constitution is favorable with a head used for a magneto-optical recording medium.
Preferably, the second slit may be formed substantially in a C-shape having two ends, and the continuity component may be disposed between the first slit and the ends of the second slit. With this constitution, the intended operation of the present invention is favorably obtained with a simple structure.
Preferably, the magnetic head of the present invention may further include an additional electroconductive film arranged in the second slit. This additional electroconductive film is electrically insulated from the first electroconductive film. This constitution makes it possible to improve the thermal conductivity between mutually opposed portions of the electroconductive films on either side of the second slit, which affords a corresponding increase in heat radiation for the electroconductive film as a whole.
Preferably, the additional electroconductive film may include two arc-shaped portions spaced apart in a radial direction of the coil, and connecting portions that link together ends of the two arc-shaped portions. The specific operation with this constitution will be described below, but induced current that would act to strengthen the magnetic field generated by the coil can be made to flow to the arc-shaped portion out of the above-mentioned two arc-shaped portions which is closer to the center of the first electroconductive film. This is favorable in that the magnetic field is strengthened.
Preferably, the first electroconductive film may be formed with a plurality of third slits extending radially of the coil, each of the third slits running from a location outside of the second slit to an outer peripheral edge of the first electroconductive film. The specific operation with this constitution will be described below, but this constitution is again favorable in that the magnetic field generated by the coil is strengthened.
Preferably, the first electroconductive film may be located opposite the recording medium with the coil therebetween and may be covered by the dielectric film. This constitution allows the coil to be closer to the recording medium than the first electroconductive film, and is therefore advantageous in terms of reducing the inside diameter of the coil and lowering its inductance when a light beam is passed through the center of this coil.
Preferably, the first electroconductive film may be provided with a thick portion protruding toward a surface of the dielectric film. This constitution enhances the heat radiation function of the electroconductive film.
Preferably, the first electroconductive film may be located closer to the recording medium than the coil. This constitution allows the first electroconductive film to be disposed in the vicinity of the top layer of the dielectric film, which again enhances the heat radiation function.
Preferably, the first electroconductive film may include two electroconductive film members that sandwich the coil in an axial direction of the coil. This constitution increases the overall volume and surface area of the two electroconductive film members, and this also improves the heat radiation function. Also, because the magnetic field generated by the coil is strengthened by the induced current flowing in the two electroconductive film members, this embodiment is also advantageous in that it promotes lower coil inductance.
Preferably, the magnetic head of the present invention may further include a slider that floats over the recording medium when the recording medium rotates. The coil and the first electroconductive film may be mounted on the slider. This constitution reduces the distance between the coil and the recording medium, and is therefore favorable for making the magnetic field act more efficiently at the specified place on the recording medium. Also, when the present invention is applied to a magneto-optical recording medium, the settings can be adjusted so that a light beam passes through the center of the coil in a state of having been focused to a quite small diameter, and this also helps reduce the coil diameter. Therefore, this embodiment is favorable for lowering the inductance of the coil. Also, the coil can be cooled by air flow between the slider and the recording medium, so the cooling efficiency is also better.
According to a second embodiment of the present invention, there is provided a data recording and reproduction device provided with a magnetic head according to the first aspect of the present invention described above.
Other features and advantages of the present invention will be clear from the following description of embodiments of the invention.